This invention relates to preprocessing and analyzing an analog signal such as a vibration signal and more specifically to a system having an analog signal preprocessor interfaced with a separate main instrument.
Sometimes the analog signal to be analyzed is a low amplitude signal which is often buried by larger amplitude signals in the noise of the analyzer or by the noise of the sensor obtaining the signal. It is difficult for an analyzer to perform an accurate analysis on the signal due to the analyzer's inability to filter out meter noise from the low amplitude signals. Thus the signal needs to be preprocessed in order to amplify or extract the signal desired so that the analyzer can perform an analysis on the signal. The function of preprocessing is to filter or amplify the input signal to allow the analyzer to optimize its performance. The preprocessor includes high pass filters, band pass filters, an envelope demodulator and amplifier circuits.
Signal processors and vibration analyzers are used for detecting defects and worn or broken parts in machinery. The analyzers are used to monitor the vibration signals from an accelerometer, electrical current signals from a current transformer or other sensor attached to a piece of machinery in order to detect these defects. These past uses functionally had the analyzer and envelope demodulator operate independently of each other. This independence proves to be a hindrance when an accurate reading is sought since each is operating according to it's predetermined manually adjusted setup.
Other problems of obtaining accurate readings include the envelope demodulator usually being comprised of only a bandpass filter and a rectifier. Typically the band pass filter is manually adjusted in order to extract the desired carrier signal to analyze. These manual adjustments are difficult to maintain due to the changing characteristics of the analog signal.
Often the analog signal's characteristics are such that only certain functions are needed to be performed on the signal to produce an optimum signal for the analyzer. This requires the ability to be flexible in the operation of the preprocessor such that only certain filtering and/or amplifying functions are to be performed.
The Hernedez U.S. Pat. No. 4,931,949 describes a method and apparatus for detecting gear defects. The apparatus includes an accelerometer which feeds a signal into an interface which then feeds a signal to an analog signal preprocessor. This analog signal preprocessor includes full wave rectifiers and low pass filters to extract an amplitude envelope. The full wave rectifiers and low pass filters are controlled by a data bus. The analog signal preprocessor amplifies the input signal and the input of the digital converter. The envelope is then converted into a digital signal to be processed by a computer. The Hernedez patent does not disclose a system which has the ability to communicate interactively between the analog signal preprocessor and the computer. Nor does the Hernedez system disclose an analog signal preprocessor which can self adjust to the input analog signal. Furthermore, the computer cannot analyze the signal without the analog signal preprocessor.
The present invention provides a system which analyzes an analog signal that utilizes an analyzer and an analog signal preprocessor. The analyzer interacts with the preprocessor to optimize the performance of the analyzer. The preprocessor has the ability to automatically adjust gain settings according to the input analog signal's characteristic. Also, the analyzer will operate without the analog signal preprocessor.
This invention overcomes the problem of inflexibility and difficulty in getting an accurate reading which will detect defects and wear. The present invention allows the analog signal preprocessor and the analyzer or computer to interact, thereby enabling the computer to setup the preprocessor according to a manual input or a predetermined program or have the preprocessor, which is smart, to autorange itself according to the input signal and relay its select range to the analyzer or computer. This allows either the operator to adjust the preprocessor or the preprocessor to adjust itself, thereby providing a more accurate and flexible means for detecting part wear and defects in machinery.